Anti-side-tone substation circuit



Jan. 16, 1923.,

1,442,427.. G. D. EDWARDS. ANTI-SIDE-TONE SUBSTATION CIRCUIT. FILED AUG-6|1919.

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Patented dan. 16, 1923.

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0F EAST ORANGE, NEW JERSEY, ASSIGNOR T0 WESTERN' ELTEC- TBJIC CUMIPANY, INCORPORATED, DF NEW YORK, N. Y., .A CORPORATIUN 019" NEW YORK.

ANTI-SIDE-TONJE 'SUBSTATIQN CIRCUIT.

pplication filed August 6, 1919. Serial No. 315,753.

T o azZZ whom t may concern.'

Be it known that 1, GEORGE D. EDWARDS, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Anti-Side- 'llone Substation Circuits, of which the following is a full, clear, concise, and exact description.

This invention relates to anti-sidetone substation circuits and more particularly to a circuit of this type which is specially adapted for use in a train despatchers substation set.

llt has for its object to provide a simple and e'icient substation circuit in which the receiver is substantially free from side tone and at the same time will be protected from low frequency signaling impulses which may be sent out on the line. Both of these requirements are important in the design,

of a telephone set which is to be used by a train despatcher who must keep the receiver continuously to his ear for long periods.

To accomplish this object a three terminal transformer winding is connected at its outer terminals to the line and onel winding of a second transformer is connected to the third terminal and to one side of the line. A line balancing resistance or network of impedances is associated with one portion of the three terminal windin vand the arrangement is such that one winding of second transformer is in shunt both to the portion of the circuit containing the line and that containing the balancing resistance. A local 'battery transmitter circuit is associated with the transformer containing the three terminal winding, and a local receiver circuit with the second transformer, this transformer being so designed that it is ecie'nt for voice currents butineicient for signaling currents. These currents, in the system described herein, are of relatively low frequency and aresent out by the train despatcher for the purpose of operating selector switches.

The invention further comprises anarrangement of condensers designed to protcct the receiver from the signa ing impulses to eectively annul the reactance of the receiver circuit, and at the same time to preline balancing network.

These and other objects of the invention.,l

will be more clearly understood from the following detailed description and claims' taken in connection with the accompanying drawings in which 1F ig. l represents diagrammatically a circuit embodying the in- Ventron; Fig. 2 is va, simplified diagram showing the current flow when transmitting, and Fig. 3 is a ,Similar view showing the current flow when receiving.

Referring tothe drawings by reference numerals, the transmitter 10 is in a local circuit including the battery 11 and the winding 12 of transformer 13. Means 14, which may be a hand operated key or a foot switch, is provided to open this circuit when the set is not in use. The other winding of transformer 13 has three terminals, the intermediate terminal 15 dividing thewinding into two parts 16 and 16. These parts will be referred to as windings 16 and 16. line wires v17 and 18 are connected to outer terminals of these windings.

The winding 19 of atransformer 20 is connected at one end to the other end to lineI wire 18. As more clearly shown in Figs. 2 and 3, winding 19 is in a bridge between the line and winding 16 on one side, and a branch including winding 16 on the other side. 1n this branch is a resistance designed to balance the resistance of the line. This resistance is indicated in Figs. 2 and 3 as a separate element by the reference numeral 33, but is preferably incorporated in the winding 16, which may be formed Wholly or in part of resistance wire. 'llhe winding 21, associated with Winding 19, is in a local circuit comprising the receiver 22, and it will be observed that both the receiver 22 and the transmitter 10 are insulated from the line by transformers.

In train despatching, an impulse transmitter of some kind is generally employed for sending out impulses to operate selector switches at a distant point. rllhese selector the a battery across the terminal 15 and at 'lav The t line b means of reversing switches 24' and 25. hese switches are operated by an electromagnet 26 which has its winding in series with the batter 27 and the makeand-break switch 28. gwitch 28 is operated by toothed disc 29. When this disc is operated, the current from battery 23 is reversed by switches 24 and 25 and impulses which may be in the form of three-cycle alternating current are sent out on the line.

To protect the receiver 22 from the above described signaling impulses, transformer 2O is designed to be ineiiicient to the frequency of these impulses and in addition a condenser 30 in the line wire 18, and a condenser 31 in the receiver circuit arel provided, both of which are inefficient to the signaling impulses, but are efficient in transmitting voice currents. The condenser 31 effectively annuls the reactance of the receiver circuit and thus increases the receiving efficiency at frequencies inthe telephonie range. A condenser 32 is placed in series with winding 16 and is designed to balance the capacity of condenserBO and may also be made to balance any capacity which the line may presentv to the substation set.

The operation of the substationset upon transmitting and receiving is shown in Figs. 2 and 3. When transmitting, currents flow in series through windings 16 and 16 and since the impedance of the line is balanced by the impedance of the branch including Winding 16, the terminals of winding 19 are at the same potential and no current flows through the bridge. On receiving, current flows through the winding 19 and is heard in receiver 22, but the rela-tion of transformer windings 12, 16 and 16 is such that no current flows through the winding 16 or the balancing resistance 33. A more complete discussion of the principles involved in designing-a set of this general type will be found in U. S. patent to G. A. Campbell, No. 1,254,47 2 dated January 22, 1918.`

What is claimed is:

1. An anti-side-tone substation circuit comprising a three terminal transformer winding adapted tovbe connected to a line, a local circuit comprising a winding inductively associated with said winding, a winding of a second transformer connected at one end to the intermediate terminal of said three terminal winding and adapted to be connected at its other end to said line, a local circuit having a winding associated with said third winding, a transmitter in one of said local circuits and a receiver in the other of said local circuits, said last mentioned circuit comprising means rendering it .efficient for telephone currents and ineflicient for low frequency signaling currents.

2. In an anti-side-tone substation set comprising a three terminal transformer winding adapted to be connected to a line, a local circuit comprising a transmitter anda winding in series, said winding bein inductively associated with said three terminal winding, a winding of a second transformer connected at one end to the intermediate terminal of said three terminal winding and adapted to be connected at its other end to said line, va local circuit comprising a receiver and a winding in series, said last-mentioned winding being associated with said third winding, and a condenser of high impedance to lowfrequency currents in series with said receiver.

3. In combination, a telephone line, means for producing low frequency currents in said line and an anti-side-tone substation set comprising a three terminal transformer winding adapted to be connected to a line, a local circuit comprising a transmitter and a winding in series, said' winding being inductively associated with said three terminal winding, a winding of a second transformer connected at one end to the intermediate terminal of said three terminal winding and adapted to be connected at its other end to said line, and a local circuit comprising a receiver and a winding in series, said last-mentioned winding being coupled with said third winding, the degree of coupling being such that telephone currents are transmitted efiiciently and low frequency currents inetiiciently and a line balancing impedance associated with the portion of the three terminal winding which is shunted by said third winding.

4. In combination, a telephone line, means for producing low frequency currents in said line and an anti-side-tone substation circuit comprising a threel terminal transformer winding adapted to be connected to a line, a local circuit comprising a transmitter and a winding in series, said. Winding being inductively associated with said three terminal winding, a winding of a second transformer connected at. one end to the intermediate terminal of said three terminal Winding and adapted to be connected at its other end to said line, a local circuit comprising a receiver and a winding in series, said lastnientioned winding being coupled with said third winding, the degree of coupling being such that telephone currents are transmitted efficiently and low frequency currents ineficiently and a line balancing resistance incorporated in the portion of said three terminal winding which is shunted by said third winding.`

5. In combination, a telephone line, means for producing lowl frequency currents in said line and an anti-side-tone substation set comprising a three terminal transformer winding adapted to be connected to a line, a local circuit comprising a transmitter and a winding in series, said Winding being inductively associated with said three terminal transformer winding a winding of a second transformer connected at one end to the intermediate terminal of said three terminal winding and adapted to be connected at its other end to said line, a local circuit comprising y'a receiver and a winding in series, said last-mentioned winding being associated with said third winding, the mutual impedance between said lastmentioned Winding and said third winding being eilicient t0 transmit currents of voice frequency but ineilicient to transmit currents of signaling frequency.

6. An anti-side-tone substation set comprising a three terminal transformer Winding adapted to be connected to a line, a 1ocal circuit comprising a transmitter and a winding in series, said winding being inductively associated with said three terminal transformer winding, a winding of a second transformer connected at one end to the intermediate terminal of said three terminal winding and adapted to be connected at its other end to Seidlne, a local circuit comprising a receiver and a Winding in series, said last-mentioned winding being associated with said third winding, the reactance of said last-mentioned local circuit being such that it is inefficient to signaling currents.

7. In an anti-side-tone substation set comprising a three terminal transformer winding adapted to be connected 'to a line, a local circuit comprising a transmitter and a winding in series said winding being indulctively associated with said three terminal transformer winding, a winding of a second transformer connected at one end to the intermediate terminal ofsaid three ter minal winding and adapted to be connected at its other end to said line, a. local circuit comprising a receiver and a winding in series, said last-mentioned winding being associated with said third denser in said last-mentioned local circuit which will transmit voice currents eiiciently but signaling currents inefiiciently.

8. The combination of a line, a loca-1 transmitter circuit and a local receiver circuit, said local circuits being inductively coupled to said line but insulated therefrom and from each other, said couplings bein so arranged that the receiver is substantially free from side tone and means in said receiver circuit to prevent low frequency currents in said line from energizing said receiver.

9. In combination, a line, a source of low equency signals connected across said line, a receiver and a transmitter associated With said line, a condenser in said line between said receiver and said low frequency source, an auxiliary network designed to balance out side tone in said receiver, said auxilia network comprising a condenser adapted to' balance ,said line condenser whereby the impedance of said auxiliary network is Iconjugate to that of the line.

l0. In combination, a line circuit and an auxiliary circuithavin a common portion, a receiver circuit assoclated with said common portion, and a condenser eiicient to transmit voice currents but inefficient to transmit signaling currents in series in each of said circuits.

In witness whereof, I hereunto subscribe winding, and a con# my name this 4th day of August, A. D. 1919. 75

GE ORGE D. EDWARDS. 

